1. Field of the Invention
This invention relates to the preparation of amines. In a particular aspect, this invention relates to the preparation of amines by reacting ammonia, a primary amine or a secondary amine with an olefin, carbon monoxide and water. In a more particular aspect, this invention relates to the preparation of amines by carrying out the said reaction in the presence of catalyst which is (a) rhodium oxide or a rhodium compound capable of forming a rhodium carbonyl and (b) iron carbonyl.
2. Description of the Prior Art
The preparation of amines by reacting an olefin with ammonia, a primary amine or a secondary amine, carbon monoxide and water, in the presence of a metal carbonyl hydride at elevated temperatures and pressures is known (for example from German Patent No. 839,800 (May 5, 1952). It has also been known to replace the carbon monoxide by ammonium formiates (German Patent No. 909,937). It has further been known to use ammonia or amines in the form of salts of phosphorus acid, sulfuric acid or carboxylic acids having more than one carbon atom, in order to avoid formation of ammonium carbonate or amine carbonates which, owing to their volatility, evolve from the liquid reaction mixture and clog the reactor pipings, (See German Patent No. 931,948). Cumbersome separation and recycling steps are necessary when the above-described methods are employed in a continuous process.
Iron pentacarbonyl has been most widely employed as the catalyst in the above-referred-to procedures. Other catalysts such as cobalt, nickel, ruthenium, iron, and copper, their compounds and alloys, moreover, fused coppersilica, cobalt chromite, cobalt-substituted amines, cobalt salts of organic carboxylic acids, nickel carbonyl and cobalt carbonyl, have also been proposed as catalysts for the aminomethylation of olefins. Copper-containing substances have been stated to be among the most active catalysts (see U.S. Pat. No. 2,497,310).
It has further been known to use amino carboxylic acids, their esters, or salts, containing at least one hydrogen atom on the amino group, as an amine reactant in the aminomethylation of ethylene and propylene (British Patent No. 803,778, filed 22.11.1956, and issued 29.10.1958).
The aminomethylation reaction for the preparation of amines has also been catalyzed by metal carbonyls or metal carbonyl hydrides, particularly iron carbonyl hydride. In the work reported by W. Reppe et al illustrating the reaction, iron carbonyl and its hydride have been exclusively as catalysts. In contrast to the known Oxo synthesis or hydroformylation, rather large quantities of the toxic iron pentacarbonyl are required, a substantial portion of which is consumed because of a release of carbon monoxide and conversion to ionic divalent iron which precipitates in the presence of carbon dioxide in the form of catalytically inactive carbonates, and oxides. The iron carbonyl thus simultaneously acts as a source of carbon monoxide. When ammonia or amines are used as reactants, the carbon dioxide formed during the reaction has to be removed continuously from the reaction gases, in order to maintain an optimum carbon monoxide pressure and thus to minimize the loss of catalyst through carbonate formation. Prolonged reaction periods are necessary for somewhat satisfactory yields.
In the procedure referred to above, only the aminomethylation of ethylene and propylene has been reduced to actual practice. The overall yields of alkylated amines in general have not exceeded 50%, when calculated on the amount of ammonia or amine originally used in the reaction. Substantial quantities of by-products such as amine carbonates, amine formiates, heterocyclic amines, amides, alcohols, aldehydes, dimers and polymers of olefin, saturated hydrocarbons, iron carbonate, iron (II) oxide and iron (III) oxide, are commonly obtained by these previous methods.
It has been suggested also that higher olefins and cyclic olefins can be brought to reaction by the above-referred-to to procedures. My attempts to extend the known iron carbonyl catalyzed synthesis to such olefinic substrates met with little success. My experimentation indicates that iron pentacarbonyl fails to catalyze to any essential extent the reaction with higher olefins.
It is also known that aminomethylation of C.sub.10 to C.sub.13 olefins can be performed with secondary alkyl amines in the presence of a cobalt carbonyl hydrocarbyl phosphine complex as catalyst. However, hydrogen has been used instead of water (U.S. Pat. No. 3,234,283). The yields of tertiary amines did not exceed 50%, based upon the olefin. Substantial quantities of the corresponding alcohol (oxo product), and also of formamide (from carbonylation of amine), aldehyde (intermediate) and saturated hydrocarbon (from hydrogenation of olefin) are indicated as having been formed as by-products.